For nine years, Stephen Colbert has relentlessly maintained his pompous, deeply ridiculous but consistently appealing conservative blowhard character on his late-night show, “The Colbert Report” — so much so that when he puts the character to rest for good on Thursday night, he may have to resort to comicide. The Grim Reaper is his last guest.

Devoted fans of “The Colbert Report” (the final T is silent) have dreaded this day since April 10, when their favorite late-night star announced that he was leaving to become the successor to David Letterman on CBS.

Mr. Colbert has steered clear of commenting on his plans for the last show, other than on-air comments that the end is near. But whatever comic exercise Mr. Colbert devises to end his multi-award-winning run on Comedy Central, including perhaps some symbolic hara-kiri for the character he brought into American homes four nights a week, he has left an indelible mark on late-night television comedy.

And he did it in a way almost no one thought was possible, or sustainable: as a fake host, a fictional character using Mr. Colbert’s own name who was an elaborate parody of a bloviating political talk show host.

Jimmy Kimmel, the host of ABC’s late-night show, with whom Mr. Colbert shares a manager (James Dixon), said he had been concerned when Mr. Colbert announced his intention to create the parody show in 2005.

“I remember pleading with Dixon to tell Stephen it was a terrible mistake to do a character the whole time,” Mr. Kimmel said. “That it wasn’t going to last, and also not to name the show ‘The Report’ as a joke. It was just going to confuse everybody. And he did, anyway, and of course, it was a smashing success in every way.”

Mr. Colbert appeared in character not simply on his show, but in appearances elsewhere, including a memorable knockout performance at the White House Correspondents’ Dinner in 2006. (He stirred Bush administration outrage with comments like: “I believe the government that governs best is the government that governs least, and by these standards, we have set up a fabulous government in Iraq.”) He even remained at his blowhard best when he testified before Congress in 2010. (Before a Congressional subcommittee on immigration issues and farm labor, Mr. Colbert’s character said things like, “Maybe the easier answer is just to have scientists develop vegetables that pick themselves.”)

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Stephen Colbert with the Grim Reaper, who is scheduled as the guest for the final episode of “The Colbert Report,” Comedy Central’s long-running late-night show.Credit
Comedy Central

Mr. Colbert has worked with many of his late-night colleagues, including Conan O’Brien and Jimmy Fallon, appearing in character, of course. (He showed up on Mr. Fallon’s debut “Tonight” show on NBC, pouring a bucket of pennies down the host’s collar, then welcoming him with a colorful phrase.)

Like other competitors, Mr. Fallon professed unabashed awe that Mr. Colbert could sustain this performance at such a high level for so long. “Before he won the Emmy, I had been preaching that people had to recognize what he was doing: He’s faking a person,” Mr. Fallon said. “I was one of those who said, ‘He’ll do it for six months and then he’ll move on.’ Imagine if you were still trying to do the Coneheads on ‘Saturday Night Live.’ It’s gets old. But not this. He’s a genius.”

But for all the effort and talent Mr. Colbert has invested in keeping the character going, he appears resolute in his intention to allow him to pass into comic history. This decision, Mr. O’Brien said, reflects tremendous confidence. “There is something really cool about Stephen saying, ‘This needs to stop at some point, so let’s stop now,’ ” he said.

In some cases, a classic comic creation defines a performer for life. Jack Benny was long associated with being a cheapskate, butchering his violin playing and lying about his age. Classic comic characters are often too fully realized to abandon.

Mr. O’Brien said that hanging on to a persona was an American convention, while British performers seem willing to walk away from their signature creations. He cited John Cleese’s Basil Fawlty and Steve Coogan’s Alan Partridge (a narcissistic media personality), though Mr. Coogan has resurrected Partridge a few times.

Ricky Gervais has also recently revived David Brent, the bumbling manager he portrayed on the British version of “The Office,” in live concert performances. “I did consider not bringing him back to life,” Mr. Gervais said. But in a new context — Brent as would-be rock star — the character could be seen as realistically having moved on.

“What’s interesting about what Colbert is doing,” Mr. Gervais said in an interview, “what’s brave and possibly confusing about it, is that he’s always used his own name.” He added: “It can be a dangerous game to play. He presented himself as the character, and now he’s not going to be it. And people are going to miss the character. It’s a joy to watch someone do a really great parody with a character saying the opposite of what you know is right.”

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Stephen Colbert’s last show on Comedy Central is Thursday night.Credit
AP Photo/Jeff Roberson

That is the essence of what is upsetting so many of Mr. Colbert’s fans. While moving up to a bigger stage is in the tradition of late-night stars pushing their careers forward — as Mr. Letterman, Mr. O’Brien and Mr. Kimmel have all done — none of those moves have required a singular comic character’s disappearing forever.

Some who have worked on “The Colbert Report” have said that Mr. Colbert was tiring of the demands of constantly staying in character, and that he had subtly been doing pieces that did not depend on it. (His recent skewering of sweep month excesses by “Good Morning, America” was a comedic tour de force with little connection to his character.)

Mr. O’Brien commended Mr. Colbert for breaking what he called the American tradition. “Our system is, if there’s another nickel to be found in it, you keep playing that character,” he said, “just beat it to death — and then do it another 10 years.”

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He added: “You always have performers saying, ‘I think I’ll go out on top, while it’s still great.’ And then it’s a sitcom, ‘Who’s the Boss?,’ and it’s the 18th season, and you’re like: ‘Tony, I like you, but ... .’ This is one of the few times when a performer is saying, ‘I want to get out while it’s still great,’ and it’s actually true.”

But going out on a slab — if that’s Mr. Colbert’s plan? “I think that’s a really funny idea,” Mr. Kimmel said. “And it would make it clear to people that he’s not that character anymore.”

Mr. Gervais agreed: “As surreal as that would be, it does make people get it. ‘I was that character, and that character is dead now. Do you get it? This is me now.’ ”

And then, presumably, Stephen Colbert can turn up next September on CBS as Mr. Letterman’s successor and be quickly accepted as a real talk show host.

“I think he’ll be great and funny, and people are going to still enjoy him plenty on that level,” Mr. O’Brien said. “And then, every now and then, there’ll be a cooking segment.”

A version of this article appears in print on December 17, 2014, on Page C1 of the New York edition with the headline: Goodbye, Nation, Goodbye, Blowhard Self. Order Reprints|Today's Paper|Subscribe